1. Field of the Invention
The invention relates to a reticle and a method of fabricating a semiconductor device through the use of the reticle.
2. Description of the Related Art
Patterns having various sizes are selected in designing layout of LSI. Hence, a mask may have both a pattern for forming a contact hole defined in a minimum design rule, such as a 0.2 xcexcmxc3x970.2 xcexcm square hole, and a pattern for forming a contact hole having a greater size, such as a 0.4 xcexcmxc3x970.4 xcexcm square hole.
When patterns for forming contact holes having various sizes are transferred to a resist, a suitable amount of light to be radiated to a resist varies in dependence on a size of a pattern. If a first pattern for forming a first contact hole and a second pattern for forming a second contact hole having a greater size than a size of the first contact hole are both exposed to light in such exposure condition that the first contact hole has a designed dimension, the second contact hole would be formed in a greater size than designed. For instance, if a first pattern for forming a 0.2 xcexcmxc3x970.2 xcexcm contact hole and a second pattern for forming a 0.4 xcexcmxc3x970.4 xcexcm contact hole are both exposed to light in such exposure condition that the 0.2 xcexcmxc3x970.2 xcexcm contact hole is properly formed, the 0.4 xcexcmxc3x970.4 xcexcm contact hole would be formed in a size in the range of 0.5 xcexcmxc3x970.5 xcexcm to 0.6 xcexcmxc3x970.6 xcexcm.
As a result, a margin between gate electrodes and a margin between field oxide films are eliminated in a contact hole such as the above-mentioned 0.4 xcexcmxc3x970.4 xcexcm contact hole. This causes a problem that a contact leak current is increased.
Hence, in a conventional method of fabricating a semiconductor device, there have been prepared two reticles in one of which a first mask is formed for patterning a contact hole having a first size, and in the other of which a second mask is formed for patterning a contact hole having a second size.
A conventional method of fabricating a semiconductor device through the use of a reticle is explained hereinbelow with reference to FIGS. 1A to 5B.
First, as illustrated in FIG. 1, there are prepared a first reticle 22 having a first pattern 21 for forming first contact holes, and a second reticle 24 having a second pattern 23 for forming second contact holes having a smaller size than a size of the first contact holes.
Then, as illustrated in FIG. 2A, positive resist 26 is coated all over a wafer 25.
Then, as illustrated in FIG. 2B, the first reticle 22 is aligned onto a pattern formed in the previous step. Then, the positive resist 26 is exposed to light, and thereafter, developed, as illustrated in FIG. 3A. Thus, the first pattern 21 for forming the first contact holes is transferred onto the positive resist 26.
Then, the wafer 25 is etched with the thus patterned positive resist 26 being used as a mask. Then, the positive resist 26 is removed. Thus, the first contact holes 27 are formed in the wafer 25, as illustrated in FIG. 3B.
Then, as illustrated in FIG. 4A, the positive resist is coated all over the wafer 25 again.
Then, as illustrated in FIG. 4B, the second reticle 24 is aligned onto the previously formed pattern. Then, the positive resist 26 is exposed to light, and thereafter, developed, as illustrated in FIG. 5A. Thus, the second pattern 23 for forming the second contact holes is transferred onto the positive resist 26.
Then, the wafer 25 is etched with the thus patterned positive resist 26 being used as a mask. Then, the positive resist 26 is removed. Thus, the second contact holes 28 having a smaller size than a size of the first contact holes 27 are formed in the wafer 25, as illustrated in FIG. 5B.
In the above-mentioned method, it seems that there may be carried out steps of aligning the first reticle 22 onto a pattern formed in the previous step, exposing the positive resist 26 to light, aligning the second reticle 24 onto the previously formed pattern without developing the positive resist 26, and developing the positive resist 26. However, this method would take much time from the first exposure till development of the positive resist 26, which would generate variance in a dimension of the positive resist 26. In particular, when a chemically amplifying resist is to be used, if it would take much time from exposure till development, there would be generated significant variance in a dimension of the resist.
In addition, when two reticles are to be used for forming contact holes having different sizes as in the above-mentioned conventional method, the number of steps for forming contact holes is two times greater than the number of steps for forming a single contact hole.
A mask used for forming a contact hole is generally aligned onto a pattern of gate polysilicon. In such alignment, there is generated misalignment both between a greater-sized contact hole and gate polysilicon and between a smaller-sized contact hole and gate polysilicon. Hence, when the greater-sized and smaller-sized contact holes are to be arranged in series, they have to be spaced away from each other by a distance including a margin corresponding to doubled misalignment. As a result, a resultant chip is unavoidable to become greater in size.
For instance, Japanese Unexamined Patent Publication No. 3-270134 has suggested a method of fabricating a semiconductor device through the use of two masks. Specifically, the suggested method includes the steps of coating photoresist onto an interlayer insulating film formed on a semiconductor substrate, exposing the photoresist to light through a first mask having a pattern for forming a first contact hole, developing the photoresist, exposing the photoresist to light through a second mask having a pattern for forming a second contact hole smaller in a diameter than the first contact hole, developing and baking the photoresist, etching the interlayer insulating film to thereby form the first and second contact holes, and forming a wiring electrode.
Japanese Patent Publication No. 5-87179 has suggested a method of making a pattern so as to form contact holes having various sizes. In accordance with the method, a mask for forming a greater-sized contact hole is designed to have a hole smaller than a designed size, taking into consideration a difference in size to be generated when a pattern is formed.
In view of the above-mentioned problems, it is an object of the present invention to provide a reticle which is capable of transferring a contact hole to a resist just in a designed dimension regardless of a size thereof.
In one aspect of the present invention, there is provided a reticle used for fabrication of a semiconductor device, including (a) a first area in which a first mask having a first pattern is formed for forming a first contact hole having a first size, and (b) a second area in which a second mask having a second pattern is formed for forming a second contact hole having a second size different from the first size.
It is preferable that the first pattern has a greater density than a density of the second pattern. Herein, a density is defined as a ratio of a total area of the first or second pattern to an area of the first or second mask.
There is further provided a reticle used for fabrication of a semiconductor device, including (a) a first area in which a first mask is formed for forming a first linear pattern having a first size, and (b) a second area in which a second mask is formed for forming a second linear pattern having a second size different from the first size.
The first size may be equal to the second size, or different from said second size. In the latter case, it is preferable that the first linear pattern has a greater density than a density of the second linear pattern.
There is still further provided a reticle used for fabrication of a semiconductor device, including N areas in each of which a first to Nth mask having a first to Nth pattern, respectively, is formed for forming a first to Nth contact hole having a first to Nth size, respectively, wherein N is a positive integer equal to or greater than 3.
It is preferable that the first to Nth patterns have different densities from one another.
There is yet further provided a reticle used for fabrication of a semiconductor device, including N areas in each of which a first to Nth mask is formed for forming a first to Nth linear pattern having a first to Nth size, respectively, wherein N is a positive integer equal to or greater than 3.
The first to Nth size may be equal to one another, or different from one another. In the latter case, it is preferable that the first to Nth linear patterns have different densities from one another, the density being defined as a ratio of a total area of a linear pattern to an area of a mask.
In another aspect of the present invention, there is provided a method of fabricating a semiconductor device, including the steps of (a) preparing a reticle having a first area in which a first mask having a first pattern is formed for forming a first contact hole having a first size, and a second area in which a second mask having a second pattern is formed for forming a second contact hole having a second size different from the first size, (b) forming a resist film on a wafer, (c) aligning the first mask to the wafer, and exposing the resist film to light, (d) aligning the second mask to the wafer without developing the resist film, and exposing the resist film to light, and (e) developing the resist film.
It is preferable that the resist film is composed of chemically amplifying resist.
It is preferable that a scanning exposure apparatus is used in the steps (c) and (d) for exposing the resist film to light.
There is further provided a method of fabricating a semiconductor device, including the steps of (a) preparing a reticle having a first area in which a first mask is formed for forming a first linear pattern having a first size, and a second area in which a second mask is formed for forming a second linear pattern having a second size different from the first size, (b) forming a resist film on a wafer, (c) aligning the first mask to the wafer, and exposing the resist film to light, (d) aligning the second mask to the wafer without developing the resist film, and exposing the resist film to light, and (e) developing the resist film.
There is still further provided a method of fabricating a semiconductor device, including the steps of (a) preparing a reticle having N areas in each of which a first to Nth mask having a first to Nth pattern, respectively, is formed for forming a first to Nth contact hole having a first to Nth size, respectively, wherein N is a positive integer equal to or greater than 3, (b) forming a resist film on a wafer, (c) aligning the first mask to the wafer, and exposing the resist film to light, (d) aligning the second mask to the wafer without developing the resist film, and exposing the resist film to light, and (e) developing the resist film.
There is yet further provided a method of fabricating a semiconductor device, including the steps of (a) preparing a reticle having N areas in each of which a first to Nth mask is formed for forming a first to Nth linear pattern having a first to Nth size, respectively, wherein N is a positive integer equal to or greater than 3, (b) forming a resist film on a wafer, (c) aligning the first mask to the wafer, and exposing the resist film to light, (d) aligning the second mask to the wafer without developing the resist film, and exposing the resist film to light, and (e) developing the resist film.
The advantages obtained by the aforementioned present invention will be described hereinbelow.
The reticle in accordance with the present invention is designed to have a first area in which a first mask having a first pattern is formed for forming a first contact hole having a first size, and a second area in which a second mask having a second pattern is formed for forming a second contact hole having a second size different from the first size. Thus, it is possible to transfer a contact hole pattern onto a resist in exposure conditions suitable for a size of a contact hole to be transferred. Accordingly, a contact hole pattern can be transferred onto a resist just in a designed dimension regardless of a size of a contact hole.
In addition, application of a resist, development of an exposed resist, and etching a wafer are carried out only once, which ensures simplification in formation of a contact hole.
In accordance with the present invention, it is no longer necessary to exchange a reticle to a different one, and hence, misregistration between a pattern for forming a greater-sized contact hole and a pattern formed in the previous step is the same as misregistration between a pattern for forming a smaller-sized contact hole and a pattern formed in the previous step. Thus, a margin between a greater-sized contact hole and a smaller-sized contact hole could be minimized.
The use of a scanning exposure apparatus enables the use of a reticle extending in a scanning direction. Hence, the first and second masks may be arranged in a scanning direction.
The above and other objects and advantageous features of the present invention will be made apparent from the following description made with reference to the accompanying drawings, in which like reference characters designate the same or similar parts throughout the drawings.